Back to EveryPatent.com
United States Patent |
5,240,567
|
Berg
,   et al.
|
August 31, 1993
|
Separation of vinyl acetate from methyl acrylate by extractive
distillation
Abstract
The separation of vinyl acetate from methyl acrylate by distillation is
difficult because of the closeness of their boiling points. Vinyl acetate
can be readily removed from methyl acrylate by extractive distillation.
Typical effective agents are phenol, methoxyethanol and isobutyl vinyl
ether.
Inventors:
|
Berg; Lloyd (1314 S. Third Ave., Bozeman, MT 59715);
Wytcherley; Randi W. (Bozeman, MT)
|
Assignee:
|
Berg; Lloyd (Bozeman, MT)
|
Appl. No.:
|
041868 |
Filed:
|
April 2, 1993 |
Current U.S. Class: |
203/57; 203/58; 203/60; 203/63; 203/64; 203/65; 203/DIG.10; 203/DIG.21; 560/218; 560/248 |
Intern'l Class: |
B01D 003/40; C07C 067/54 |
Field of Search: |
203/57,58,60,63,64,65,DIG. 10,DIG.21
560/248,218
|
References Cited
U.S. Patent Documents
2171795 | Sep., 1939 | Kautter | 203/65.
|
3691021 | Sep., 1972 | Feldman et al. | 560/248.
|
3736236 | May., 1973 | Di Fiore et al. | 560/248.
|
4897161 | Jan., 1990 | Berg et al. | 203/51.
|
4925533 | May., 1990 | Berg | 203/51.
|
Foreign Patent Documents |
45-36887 | Nov., 1970 | JP | 560/218.
|
47-37929 | Sep., 1972 | JP | 560/218.
|
Primary Examiner: Bascomb, Jr.; Wilbur
Claims
We claim:
1. A method for recovering vinyl acetate from a mixture of vinyl acetate
and methyl acrylate which comprises distilling a mixture of vinyl acetate
and methyl acrylate in a rectification column in the presence of about one
part of an extractive agent per part of vinyl acetate - methyl acrylate
mixture, recovering the vinyl acetate as overhead product and the methyl
acrylate and the extractive agent from the stillpot, wherein said
extractive agent consists of one material selected from the group
consisting of adiponitrile, sulfolane, phenol, o-cresol, m-cresol,
p-cresol, 2-tert. butyl phenol, 2,4-di-tert. amyl phenol, 2,6-dimethyl
phenol, 4-ethyl phenol, 1-propanol, isodecyl alcohol, sec. phenethyl
alcohol, cyclopentanol, methoxyethanol, propylene glycol phenyl ether,
isobutyl vinyl ether and nitrobenzene.
Description
FIELD OF THE INVENTION
This invention relates to a method for separating vinyl acetate from methyl
acrylate using certain higher boiling liquids as the agent in extractive
distillation.
DESCRIPTION OF PRIOR ART
Extractive distillation is the method of separating close boiling compounds
from each other by carrying out the distillation in a multiplate
rectification column in the presence of an added liquid or liquid mixture,
said liquid(s) having a boiling point higher than the compounds being
separated. The extractive agent is introduced near the top of the column
and flows downward until it reaches the stillpot or reboiler. Its presence
on each plate of the rectification column alters the relative volatility
of the close boiling compounds in a direction to make the separation on
each plate greater and thus require either fewer plates to effect the same
separation or make possible a greater degree of separation with the same
number of plates. The extractive agent should boil higher than any of the
close boiling liquids being separated and not form minimum azeotropes with
them. Usually the extractive agent is introduced a few plates from the top
of the column to insure that none of the extractive agent is carried over
with the lowest boiling component. This usually requires that the
extractive agent boil about twenty Celcius degress or more higher that the
lowest boiling component.
At the bottom of a continuous column, the less volatile components of the
close boiling mixtures and the extractive agent are continuously removed
from the column. The usual methods of separation of these two components
are the use of another rectification column, cooling and phase separation,
or solvent extraction.
Extractive distillation would be an attractive method of effecting the
separation of vinyl acetate from methyl acrylate if agents can be found
that (1) will create a large apparent relative volatility between vinyl
acetate and methyl acrylate and (2) are easy to recover from the methyl
acrylate, that is, form no azeotrope with methyl acrylate and boil
sufficiently above methyl acrylate to make separation by rectification
possible with only a few theoretical plates.
Extractive distillation typically requires the addition of an equal amount
to twice as much extractive agent as the vinyl acetate--methyl acrylate on
each plate of the rectification column. The extractive agent should be
heated to about the same temperature as the plate into which it is
introduced. Thus extractive distillation imposes an additional heat
requirement on the column as well as somewhat larger plates. However this
is less than the increase occasioned by the additional agents required in
azeotropic distillation.
Another consideration in the selection of the extractive distillation agent
is its recovery from the bottoms product. The usual method is by
rectification in another column. In order to keep the cost of this
operation to a minimum, an appreciable boiling point difference between
the compound being separated and the extractive agent is desirable. We
recommend twenty Celcius degrees or more difference. It is also desirable
that the extractive agent be miscible with overhead products otherwise it
will form a two phase azeotrope with them and some other method of
separation will have to be employed.
Vinyl acetate, B.P.=72.7.degree. C. and methyl acrylate, B.P.=80.3.degree.
C. boil so close together that the relative volatility is only 1.3. Table
1 shows that the separation by conventional rectification requires 42
actual plates to get 99% purity. With an agent giving a relative
volatility of 1.9, only 20 actual plates are required.
TABLE 1
______________________________________
Theoretical and Actual Plates Required vs. Relative
Volatility for Vinyl Acetate - Methyl Acrylate Separation
Relative
Theoretical Plates Required
Actual Plates Required,
Volatility
At Total Reflux, 99% purity
75% Efficiency
______________________________________
1.3 35 47
1.5 23 31
1.8 16 21
1.9 15 20
______________________________________
OBJECTIVE OF THE INVENTION
The object of this invention is to provide a process or method of
extractive distillation that will enhance the relative volatility of vinyl
acetate from methyl acrylate in their separation in a rectification
column. It is a further object of this invention to identify organic
compounds which in addition to the above constraints, are stable, can be
separated from methyl acrylate by rectification with relatively few
theoretical plates and can be recycled to the extractive distillation
column and reused with little decomposition.
SUMMARY OF THE INVENTION
The objects of this invention are provided by a process for separating
vinyl acetate from methyl acrylate which entails the use of certain
organic compounds as the agent in extractive distillation.
DETAILED DESCRIPTION OF THE INVENTION
We have discovered that certain organic compounds will greatly improve the
relative volatility of vinyl acetate to methyl acrylate and permit the
separation of vinyl acetate from methyl acrylate by rectification when
employed as the agent in extractive distillation.
TABLE 2
______________________________________
Effective Extractive Distillation Agents
Compounds Relative Volatility
______________________________________
None 1.3
Adiponitrile 1.4
Sulfolane 1.4
Phenol 1.8
o-Cresol 1.7
m-Cresol 1.7
p-Cresol 1.8
2,4-Di-tert amyl phenol
1.6
2-tert. Butyl phenol
1.4
2,6-Dimethyl phenol
1.6
4-Ethyl phenol 1.7
1-Propanol 1.4
Propylene glycol phenyl ether
1.4
Isodecyl alcohol 1.4
sec. Phenethyl alcohol
1.4
Cyclopentanol 1.5
Methoxyethanol 1.9
Isobutyl vinyl ether
1.6
Nitrobenzene 1.4
______________________________________
Table 2 lists the compounds that we have found to be effective. They are
adiponitrile, sulfolane, phenol, o-cresol, m-cresol, p-cresol, 2-tert.
butyl phenol, 2,4-di-tert. amyl phenol, 2,6-dimethyl phenol, 1-propanol,
4-ethyl phenol, propylene glycol phenyl ether, isodecyl alcohol, sec.
Phenethyl alcohol, cyclopentanol, isobutyl vinyl ether, methoxyethanol and
nitrobenzene.
THE USEFULNESS OF THE INVENTION
The usefulness or utility of this invention can be demonstrated by
referring to the data presented in Tables 1 and 2. All of the successful
agents show that vinyl acetate can be separated from methyl acrylate by
means of extractive distillation in a rectification column and that the
ease of separation as measured by relative volatility is considerable.
WORKING EXAMPLES
Example 1
Fifty grams of vinyl acetate,50 grams of methyl acrylate and 50 grams of
phenol were charged to an Othmer type vapor-liquid equilibrium still and
refluxed for thirteen hours. Analysis of the vapor and liquid by gas
chromatography gave a vapor composition of 57.4% vinyl acetate, 42.6%
methyl acrylate and a liquid composition of 43.3% vinyl acetate, 56.7%
methyl acrylate. This indicates a relative volatility of 1.8.
Example 2
Fifty grams of vinyl acetate, 50 grams of methyl acrylate and 50 grams of
methoxyethanol were charged to the vapor-liquid equilibrium still and
refluxed for three hours. Analysis gave a vapor of 67% vinyl acetate, 33%
methyl acrylate and a liquid composition of 51.3% vinyl acetate, 48.7%
methyl acrylate. This indicates a relative volatility of vinyl acetate to
methyl acrylate of 1.9.
Top